So I found the answer by trying to export my map in TileMill :
To get the whole world, starting from zoom 0, if you play with zoom max, here are the given estimations :
- Zoom 15 à 22 ==> 1000 Gb+
- Zoom 12 à 14 ==> 100 Gb+
- Zoom 11 ==> 10 Gb+
- Zoom 10 ==> 1 Gb+
- Zoom 9 ==> 100mb
- Zoom 8 ==> 10mb
- Zoom 7 ==> 1mb
- Zoom <7 ==> <1mb